Orthopedic devices are artificial devices used to replace or strengthen a particular part of the body. Such devices can be used in humans or animals to repair or replace diseased or damaged bone, allied tissue associated with the bone, and/or joints associated with the bone. Primarily, orthopedic devices are used to correct or prevent skeletal deformities or injuries and to alleviate the pain and discomfort associated with the deformities or injuries.
When implanting a prosthesis, typically a receiving site or cavity is first prepared in an adjoining bone. In particular, the bone can be cut and reamed out in order to accommodate the prosthesis. A bone cement is then mixed and placed in the receiving site or cavity. A prosthesis is positioned in the bone cement, and the bone cement is subsequently cured and hardened affixing the prosthesis to the bone.
Once implanted, an orthopedic device ideally closely assimilates the characteristics of the bone and/or the joint that the device is intended to repair or replace. The implanted orthopedic device should be capable of supporting and withstanding stresses and strains normally imparted to the repaired or replaced bone joints.
In the past, many orthopedic devices were made from metals, such as stainless steel, titanium, and cobalt chrome alloys. Metal devices, however, tend to be less flexible and more rigid than bone material. Thus, those skilled in the art have attempted to design orthopedic devices made from polymer materials that have physical properties more similar to the physical properties of bone. For instance, ultrahigh molecular weight polyethylene has been incorporated into orthopedic devices.
In the past, polyoxymethylene polymers have also been used to produce orthopedic devices including trial sizers for joint replacement parts such as for the hip and knee. When used as a trial sizer, the orthopedic device may be reused during different operations. At the end of each use, the orthopedic device may be steam sterilized. Unfortunately, various problems have been experienced with the polyoxymethylene polymer composition. For instance, prior polyoxymethylene polymer compositions have a tendency to generate agglomerates that adversely interfere with the appearance of the device, especially when the device is color coded. In addition, blooming has occurred on the polyoxymethylene polymer devices after multiple sterilizations, which appear as white spots on the surface of the device. In view of the above, a need exists for a polymer composition, and particularly a polyoxymethylene polymer composition, for producing orthopedic devices, including trial sizers.